Nitrogen is a major constituent of proteins and enzymes that regulates photosynthetic capacity in plants. We use a novel approach for nitrogen allocation (N-allocation) that aims to maximize photosynthesis by allocating nitrogen in plant leaves in two steps: (i). vertical distribution of leaf nitrogen based on an optimal exponential distribution through the vertical canopy structure, and (ii). balancing the leaf-level nitrogen between chlorophyll and rubisco to maintain the photosynthetic rate. We incorporated this N-allocation approach in a multilayer canopy‐soil‐root system model (MLCan) that was then validated for maize (C4) using observed data at Urbana, Illinois, USA. The model evaluation shows that the N-allocation method established the coupling between ecohydrological processes and soil-nitrogen dynamics. The simulation results indicated the strength of feedback between leaf-level nitrogen and eco-physiological processes. This relationship was affected by changes in the fertilizers and key climatic variables such as CO2, precipitation and ambient temperature. The sensitivity of temperature increased after the implication of the N-allocation method. The vertical profiles of net photosynthetic rate (An) were resolved based on the vertical distribution of photosynthetic nitrogen. The increase in temperature lowered the vertical gradient of photosynthetic nitrogen and in response, the vertical profile of was reformed.